It has been known since antiquity that the brain is composed of two hemispheres, and people have been attempting for centuries to exploit this fact in explanations of psychological function. By the middle of the 19th century, neurologists had begun to understand that the left hemisphere was dominant for language. In this century, scientists have found the right hemisphere to be dominant for other abilities, such as the understanding and expression of emotion. This partial independence of hemispheres was confirmed in split brain experiments in animals and later in humans showing that hemispheric specialization and partial hemispheric independence could exist together. Research has found that in normal persons the right brain has intelligence and autonomous mental functions separate from those of the left brain.
The right brain and left brain are capable of having their own mentation and actions. Observations have indicated that the cognitive faculties of the right brain in split brain and left-hemispherectomy patients can be fully developed. An isolated right hemisphere has the capacity for autonomous perception, memory, thought, emotion and volition. The right brain, in split-brain patients, can also induce or affect behavior without a correct conscious, left-sided understanding of the reason behind it. In normal individuals, the right hemisphere can have intact mental faculties, separate from and often beyond the awareness of the patient's left-sided mind.
Therefore, a need exists for an apparatus and method that can stimulate a subject by changing the side of the brain which predominates to achieve a change in the psychological state of the subject.